Home – Home – Jornals – Chemistry for Sustainable Development 2022 number 5

Prediction of the physical-mechanical properties of metallurgical coke is an essential task from the viewpoint of its efficient application in the blast furnace process, in chemical industry, and also as fuel. The development of this task is the physical substantiation of the formation of coke piece strength. A method based on gasification is proposed to evaluate the size distribution of molecular oriented domains L_с(lamella height) and L_a(lamella length) indexes. It has been established through the analysis of the structure of large and small domains that large domains are less reactive in comparison with the small ones. For this reason, it is possible to use gasification with carbon dioxide to remove small domains leaving the large domains within the coke pieces. Results of the experiments provide evidence that mainly large domains remain in coke pieces after gasification. The indexes L_с and L_a were determined to increase approximately by a factor of 1.5 after gasification.

Elastic cryogels of rubber-like consistency were formed from a two-component solution of polyvinyl alcohol in water after a freeze-thaw cycle. Interest in these ecologically friendly polymer cryostructurates with their inherent viscoelasticity is due to their high potential as structural materials in oil mining and construction industry. Cryogels based on the aqueous solution of polyvinyl alcohol containing the particles of soil or fine coal as the dispersed phase, as well as emulsified mineral oil waste, are proposed for practical use. The rheological characteristics of the polymer solution and the direct emulsion based on it are investigated, along with the elastic and waterproofing properties of filled cryogels. It is demonstrated that the materials based on multicomponent cryogels possess increased elasticity and good waterproofing properties, which allows them to be used as the materials for impervious screens in hydraulic structures. Cryogels were obtained after cryostructuring of the suspension of fine coal in the aqueous solution of polyvinyl alcohol, and their drying resulted in obtaining fuel briquettes with high physical, mechanical, and energy characteristics. These briquettes may be used for domestic and industrial properties. To solve environmental problems, a methodology for soil reclamation and development of a stable vegetation cover on the territory of mine facilities is proposed.

The reaction of hydrogen transfer from coal tar pitch and petroleum pitches to α-methylstyrene with the formation of cumene was investigated in glass ampoules within the temperature range of 200-360 °C and reaction time of 15-60 min and when passing α-methylstyrene through a layer of coal tar pitch. It is shown that the formation of non-chromatographable products of α-methylstyrene condensation with polycyclic aromatic compounds of pitches occurs simultaneously. The dependences of α-methylstyrene conversion, the selectivity for cumene and condensation products on the temperature and reaction time, the ratio of pitch/α-methylstyrene are determined. The amount of hydrogen transferred from pitches to α-methylstyrene was determined, and the results obtained were compared with the literature data on the transfer of hydrogen from pitches obtained using anthracene as a hydrogen acceptor.

A systematic study of the relationship between the composition and structure of skeletal-dendritic ferrospheres isolated from fly ash formed in the combustion of Ekibastuz coal, carried out by means of scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), allowed us to establish the general routes of their formation and the peculiarities of the influence of mineral precursors on their structure. The groups of globules were distinguished exhibiting a linear correlation between the content of silicon, iron and aluminium oxides in the gross composition of the polished sections. It is shown that the investigated ferrospheres are formed from the melt droplets of the general FeO-SiO₂-Al₂O₃-CaO system during their cooling and crystallization of individual phases. The formation of melt droplets occurs due to the sequential transformation of dispersed products from thermal conversion of mineral precursor associates, such as siderite, quartz, calcite and aluminosilicate components in the carbon matrix. The aluminosilicate precursor determining the structure of globules is hydromica of illite group. The crystallization of the ferrospinel of skeletal-dendritic globules occurs due to the “seed” of Al,Mg-ferrospinel, which is formed as a result of the thermochemical transformation of the illite of the initial coals. The observed general trend to changes in the structure of ferrospheres from coarse-grained crystalline skeletal type to fine-crystalline skeletal-dendritic globules is explained by a decrease in the content of the main spinel-forming oxides FeO, Al₂O₃ and MgO in the melt microdroplets.

Results of the classical method for determining the tendency of coals to spontaneous ignition from the rate constant of oxygen sorption are compared with those obtained using the improved method of thermogravimetric analysis (TGA). To study the sorption capacity of the studied coal samples by thermogravimetric analysis, it is proposed to heat the samples at a constant heating rate of 5 °C/min to 300 °C instead of high temperatures (1000 °C), implying coal combustion. The chemical activity of coal samples with respect to oxygen is to be calculated from the maximum mass gain within the temperature range corresponding to oxidation. As a result of the experiment, on the basis of thermogravimetric dependences, differences were revealed in the behaviour of coal samples, prone and not prone to spontaneous ignition. In comparison with the classical V. S. Veselovsky’s method of determining the tendency of coals to spontaneous ignition, the TGA method allows one to get a more complete picture of the chemical activity of coals, which affects the reliability of assigning the analyzed sample to the category of spontaneous ignition hazard.

Because of the high level of cardiovascular diseases in the Kemerovo Region, it is extremely important to reveal a relation between exposition to dust from the coal industry and human health. One of the first steps for this disclosure is investigation into the physical and chemical properties of dust in the hospitals of Kemerovo (Kemerovo Region - Kuzbass), which is reported in this paper. It is found that the object analysed is a mixed type, not uniform, and contains organic and inorganic parts. The major mineral part is silica, which agrees with its content in fly ashes characteristic of the region. Constant concentration ratios of aluminium, silicon and manganese allow an assumption that the dust is built up by similar types of aluminosilicates containing manganese within the structure. Low amounts of sulphur and high amounts of calcium simultaneously indicate the presence of calcite and/or feldspar in the dust. High contents of sodium and calcium can be caused by the application of detergents. The dust is classified as PM_0.1-PM₁ according to particle sizes. The relationship of the properties of dust with the characteristics of the industrial orientation of the region is outlined.

Nanostructured composites obtained by forming a filler (Co₃O₄ nanoparticles) during thermal decomposition of two kinds of precursors (Co(N₃)₂ and Co(OH)₂) in the air on the surface of carbon matrices with significantly different morphology (single-walled carbon nanotubes and highly porous material from raw coal) are characterized, and the influence of matrix type on composite properties is considered. It is established that the characteristics holding the greatest significance for electrode materials, that is, the distribution of filler particles over composites, their sizes, matrix stability against oxidation, and, most importantly, the electrical capacitance characteristics of composites, are determined first of all by matrix morphology. This relationship manifests itself in the regularities of matrix oxidation during the formation of Co₃O₄ nanoparticles within its volume, acting as a catalyst for this process. Highly porous matrix is most prone to oxidation, and for this reason an increase in filler content and oxygen concentration is observed in the subsurface layers, which leads to a substantial decrease in electrical capacitance. In composites based on almost non-oxidized multiwall C-tubes, a noticeable increase in capacitance occurs due to the contribution of Red-Ox electrode processes involving Co₃O₄ particles. Composites based on single-walled C-tubes coalesced into dense “ropes” occupy an intermediate position.

The TUBALL material consisting of single-walled carbon nanotubes (SWCNTs) is characterized. The features of the formation of nanostructured composites through the reduction of HAuCl₄ solutions by the matrix (carbon) on the outer surface of coalesced nanotubes are considered, their morphology and the features of occurrence of thermally stimulated processes are studied, as well as their electrochemical properties in supercapacitor (SC) model cells. According to transmission electron microscopic data, the incorporated gold nanoparticles are probably shaped as flattened ellipsoids with particle size of 6-30 nm (30-40 nm according to X-ray diffraction data) and are located on the surface of “ropes”, which are close-packed ensembles of parallel SWCNTs. According to the results of sorbometry, the internal channels of SWCNT (1-2 nm) and extended pores between them are accessible to sorbed nitrogen, but inaccessible to the precursor solution. The sizes of coherent scattering regions, estimated from the broadening of X-ray diffraction reflections, turned out to be larger than particle sizes determined by means of TEM, which is due to their anisometric nature. The study of thermally stimulated processes in composites shows that gold deposition on the SWCNT surface leads to an increase in the stability of C-matrix against oxidation. Investigation of Au/SWCNT nanocomposites as electrode materials for supercapacitors shows that decorating the surface of SWCNT “ropes” with gold causes a significant decrease in the active component of the impedance and an increase in the electric capacitance of the SC cells in the region of high potential scanning rates, as a consequence of an increase in charge density at TUBALL/Au/electrolyte interfaces during polarization, and a decrease in electric resistance. The greatest effect (an increase in capacity by a factor of 3.0-3.5) was observed for the nanocomposite electrode 2 wt. % Au/SWCNT.

In this work we studied the effect of pulsed nanosecond laser radiation (532 nm, 14 ns, 6 Hz, 0.2-0.6 J/cm²) on brown coal samples in an argon atmosphere. H₂, CH₄, C₂H₂, CO and CO₂ were found in the composition of gaseous products formed in the pyrolysis of coal samples. It is shown that with an increase in the laser radiation energy density, the volume fraction of acetylene in the composition of gaseous products of coal pyrolysis increases, while the volume fractions of methane and carbon dioxide, on the contrary, decrease. The volume fractions of hydrogen and carbon monoxide in the studied range of laser radiation energy density are close to constant. The volume of combustible gases formed per unit mass of the reacted coal sample increases with increasing laser radiation energy density in the range of 0.2-0.5 J/cm². With a further increase in the energy density of laser radiation, the volume of combustible gases formed per unit mass of the reacted coal sample remains practically unchanged.

Results of investigation into the composition of humic acids (HA) and fulvic acids (FA) isolated from brown coals by means of proximate and ultimate analysis, IR, and EPR spectroscopy are presented. It is shown that the yield of HA exceeds the yield of FA. The maximum yield (60-68 %) was detected for HA from naturally oxidized brown coal. It has been established that lignite FA and HA have significant differences in the structural and group composition: FA are characterized by the higher content of the fragments of aliphatic structures, alcohols, carboxylic acids, and esters. Humic acids are characterized by the higher content of aromatic fragments.

Carbon sorbents were obtained at different ratios of coal/alkali from coals of the Kaa-Khem, the Mezhegey and the Elegest deposits. It is established that the necessary mass ratio of coal/alkali for these coal samples at the activation stage is 1 : 3 or 1 : 4. The excess alkali concentration worsens textural characteristics. It is shown by means of IR spectroscopy and thermogravimetry that alkaline treatment causes chemical changes in the molecular structure: the content of oxygen-containing fragments increases, the amount of carbon in aromatic structures decreases, which causes a decrease in caking capacity. The revealed features include a significant decrease in the final temperature and narrowing of the interval of the main decomposition of the coal organic mass, changes in the mass loss curves within the temperature range of 500-750 °C, corresponding to the zone of decomposition of the aromatic structures in coal. Physicochemical regularities of material formation and optimal conditions providing the production of sorbents with high texture characteristics from sintering coals were determined. On the basis of the studies of adsorption characteristics of the samples (for iodine and methylene blue), it is concluded that it is reasonable to use the obtained carbon sorbents for the purification of industrial wastewater from organic pollutants (phenol, pyridine, etc.).

Based on the results of adsorption studies, a procedure for modifying the porous carbon sorbent with tributyrin has been developed. The synthesis of tributyrin and the procedure of its quantitative determination in ethanol solutions by means of spectrophotometry are described. Carbon sorbent samples modified with tributyrin were obtained. Their properties have been studied using a complex of physicochemical methods. The possibility of using the modified sorbent as a drug of prolonged action is studied: tributyrin desorption from the carbon sorbent under model conditions in contact with 0.9 % NaCl (physiological solution) and in ethanol is investigated. It is established that in contact with the test solutions, the modifier deposited on the carbon carrier is desorbed within 6 h.

Methods of scanning electron microscopy, NMR spectroscopy, XRD, thermal analysis and gas chromatography-mass spectrometry have been used to study the composition, structure and morphology of particles of α₂-fraction powders isolated by the method of selectively soluble groups from medium-temperature coal-tar pitch. It is shown that the α₂-fraction is mainly a mixture of condensed aromatic compounds containing N, O and S heteroatoms, while sulphur is mainly contained in the form of heat-resistant thiophene compounds. The study of coke particles formed during the thermolysis of the α₂-fraction showed that in the temperature range from 300 to 600 ^oC, a dense structure with carbon content 90-93 % is formed from the substances of the α₂-fraction. Further heating up to 1200 ^oC leads to an increase in the carbon content up to 97 %, while the coke particles form a layered structure with pronounced anisotropy, approaching the structural characteristics of L_a and L_c to “premium class” needle cokes.

The dispersed fractions of industrial high-calcium fly ash (HCFA), selectively collected in the form of fractions 1-4 (Fr1-Fr4) on fields 1-4 of the electrostatic precipitators of the ash collecting unit at the Krasnoyarsk TPP-2, are systematically characterized. The fluidity parameters of ash mortars prepared from 100 % of each of the fractions at a ratio of water/binder = 0.5 were determined. It has been established that the value of fluidity decreases with an increase in the specific surface area of the fractions from Fr1 to Fr4. The parameters of cement-ash mortars with the replacement of cement by 50 and 20 % of each of the four fractions were determined. It has been established that at a 20 % HCFA content, the fluidity of cement-ash mortars of all fractions meets the requirements of GOST 1581-2019 for oil well cements. The samples based on finely dispersed fractions Fr3 and Fr4 meet the requirements for compressive strength on the second day of hardening. The specimens of ash-cement composites with high strength, more than 50 MPa for the 28th day of hardening, were prepared on the basis of the Fr4 fraction. In particular, high compressive strength (62-90 MPa) has been achieved for composite cements containing 80 and 90 % of the Fr4 fraction of HCFA in the presence of the superplasticizer Melflux 5581 F, which promotes efficient dispersion of finely dispersed HCFA in the liquid phase, faster and more complete interaction of active components with the formation of hardening hydrated phases. The addition of 5 % microsilica, which promotes the formation of an additional amount of calcium hydrosilicates, made it possible to achieve an increase in strength up to 108 MPa. The results obtained show that finely dispersed HCFA can be used as the components of oil well cements to improve the flowability of cement-ash slurries and improve the strength properties of highly filled ash-cement composite materials.

It is shown that the yield of humic acids increases by 20-30 % during the mechanical treatment of coals with a complex of oxidative-alkaline reagents. Upon the mechanochemical oxidation of the organic matter of brown coals, the molecular weight of humic acids and the percentage of aliphatic fragments in their structure decrease, while the content of phenolic and carboxyl groups increases. Ion exchange processes during the mechanical treatment of coals with mineral salts are accompanied by a decrease in the content of Na⁺ cations and an increase in Ca²⁺, Mg²⁺ cations in the composition of water-soluble humic substances. The concentration of SO₄^2- ions increases in samples of humic substances obtained from coals after mechanical treatment with ammonium sulphate.

The urgent problems of decarbonization in the power-generating sector are analyzed, along with the potential routes to solve ecological problems connected with CO₂ evolution from the combustion of coal - one of the major kinds of fuel for power generating facilities in the world, and especially in Russia and in Kazakhstan. The technology and equipment of the technological line for low-temperature (not higher than 75 °C) hydroconversion of power-generating coal into high calorific (heat of combustion 45 MJ/kg), ecologically safe (purified from ash) liquid hydrogenated coal fuel (HCF) with low carbon content (less than 45 %) are described. The methods for processing coal fuel in the form of water-coal suspension are considered. The routes to conserve the coal industry are discussed, relying on the production of hydrogenized coal fuel with low prime cost from power-generating coal, which will ensure technologically efficient and ecologically safe transition to low-carbon power engineering with zero greenhouse gas emission.

The history of processes for obtaining synthetic fuels by liquefying coals is described. Coal processing technologies are analyzed since the time of F. Bergius up to the present day. Modern hydrogenation processes are described. The basics of single-stage coal liquefaction technologies are described: Kohleoel (Ruhrkohle, Germany), NEDOL (NEDO, Japan), H-Coal (HRI, USA), Exxon Donor Solvent (ExxonMobil, USA), and Solvent Refined Coal (SRC-I and SRC-II, Gulf Oil, USA), as well as two-stage technologies for producing synthetic liquid hydrocarbons from coal: Brown Coal Liquefaction (NEDO, Japan), Catalytic Two-stage Liquefaction (DOE, HTI, USA), Integrated Two-stage liquefaction (Lummus, USA) , Liquid Solvent Extraction (British Coal Corporation, UK), Supercritical Gas Extraction (British Coal Corporation, UK). The scientific foundations of the processes for obtaining biochars from different kinds of biomass by means of hydrothermal carbonization are described. The existing technologies based on this process are indicated. The possibility to upgrade modern coal chemistry in line with “green chemistry” by integrating biomass and the products based on it into coal chemical processes is shown.